Whether Horizontal or Vertical the reason it is called Form Fill and Seal is because part of the bag or wrapper is being formed off a continuously fed roll of wrapping material as the product is added to the bag. As the product is added to the bag the rest of the bag is literally formed around the product and sealed. The seal not only closes the end of the newly formed bag, it also creates the leading edge of the next bag too, and the process begins again. Hence the term 1) FORM 2) Fill 3) SEAL, and that is where the similarity ends.
This machine without a doubt produces the most popular type of packaging in use today on the planet earth. There a probably more of these types of machines out there making packages than any other type. Why? Because they use a free source of power, which is gravity. Many products out there are sold in measured units of weight or volume. Automatic Weigh Scales or Volumetric feeders collect the product in bulk and then dispense it out in weighed or measured batches to the vertical form fill seal machine waiting below. Common examples of the vertical process are all the potato chip type snack bags that you see in almost every food store you go to.
On this machine electronic signals are used to control the synchronization between the product dispenser and the bag maker so that product is not dropped while a seal is being formed or vice versa. The machine you see above is a Wright brand VFFFSM, which had the electrics rebuilt by me so it could be used once again. You can also go to the tab on BAGGING machines and view a slide show of the Hayssen Ultima VFFSM, which is one of the best machines of this type in use in the world today.